1. Field of the Invention
The present invention is in the field of computer hardware and specifically relates to a novel card edge conductor pattern and card edge connector that permits 114 conductors to be connected to the card, instead of the conductors used in the earlier 8-bit STD card.
Cards of the new design can be used with connectors of the earlier type (although only 56 conductors will be connected to the card) and the new card edge connector will accept cards of the earlier standard design (although again only 56 conductors will be connected to the card).
By use of the new card edge conductor pattern and card edge connector it is possible to build computers which have the capability of operating with 32-bit words but which also are compatible with earlier 8 and 16-bit STD cards. Conversely, the new card edge conductor pattern and card edge connector can be used in 8 and 16-bit computers to provide for later upgrading to 32 bits.
2. The Prior Art
Brief acquaintance with the wiring diagrams of computers suggests that computers consist of processing circuits that are interconnected by a set of conductors. Some of the conductors are utilitarian and supply such housekeeping quantities as power and standard voltage levels including ground. Others of the conductors are bearers of reference quantities such as clock signals, timing signals, and signals that indicate the instantaneous state of the computer. Still others of the conductors carry signals representing data that is needed simultaneously in various parts of the computer. Together, these interconnecting conductors are called a bus.
Instead of being mere conductors, the processing circuits operate on some of the signals they receive from the bus to produce other signals which they apply to the bus. Traditionally, the processing circuits have been developed and produced separately on individual printed circuit boards, also called cards.
It is not difficult to visualize the bus as a sort of spinal cord of the computer and the processing circuits as the various bodily organs that are connected to it.
This imagery leads understandably to a computer architecture in which a stack of spaced and parallel cards are distributed along a one-dimensional, usually linear, bus. The whole computer fits neatly into a rectangular box.
Mechanically, one edge of each card fits into a socket in a card edge connector. The edge of the card includes a number of conductive fingers that are etched on the card and that extend perpendicular to the edge. Each conductive finger is contacted by a pin in the card edge connector, and is thereby connected electrically to a particular conductor in the bus. Normally the same pattern of conductive fingers is produced on both sides of the card adjacent the same edge, and the card edge connector includes a first set of pins that contacts the fingers on a first side of the card and a second set of pins that contacts the fingers on the second side of the card.
At present more than 1000 different processing circuits are available in card form from various manufacturers, and these all have identically the same standard finger pattern known as the 8-bit STD pattern, shown in FIG. 1. The corresponding bus is called the 8-bit STD Bus.
Introduced in 1978, the STD Bus is now the second most widely used industrial bus standard in the United States. An approved IEEE Standard, it provides a well-documented and supported modular approach for designing test and control systems. Rugged, easy to implement, and cost effective, STD Bus systems are being used at an increasing rate as this Standard enters its eleventh year.
However, a demand is developing for higher performance systems that are more computation-intensive. These systems require a bus that can accommodate 32-bit words rather than the 8-bit words used with the 8-bit STD Bus.
The present invention addresses the need for a 32-bit bus that retains the attractive characteristics of the 8-bit STD Bus and at the same time is backward-compatible with the more than 1000 8-bit STD cards currently available.
Thus, the present invention, in providing a growth path from 8-bit to 32-bit data does more than merely add more fingers to the cards and pins to the card edge connectors, although these are necessary. The significant accomplishment of the present invention is to provide a 32-bit Bus that is compatible with the more than 1000 8-bit STD Bus cards currently available. This permits users of the 32-bit bus of the present invention to capitalize on the enormous variety of cards available in the 8-bit STD Bus format while keeping open a growth option to 32-bit performance.
In U.S. Pat. No. 4,934,961 issued June 19, 1990 to Piorunneck, et al, there is described a bi-level connector for making mechanical and electrical contact between a mother printed circuit board and a daughter printed circuit board. The connector, as best seen in FIGS. 13 and 14 of the patent, uses alternating short and long contact pins which contact the daughter printed circuit board at different distances from its inserted edge. In contrast, in the present invention, the contact pins of the connector are identical. The connector of Piorunneck, et al. is described as having backward compatibility in the sense that their new connector will accommodate an older type of circuit board. However, their new type of circuit boards cannot be used in old type connectors; thus, unlike the present invention, the invention of Piorunneck, et. al. lacks forward compatibility. The patent includes a lengthy listing of the prior art.